Salmonellosis is one of the most common causes of acute gastroenteritis. During this infection, Salmonella enters its host preferentially through the Peyer's patches of the terminal ileum. The Peyer's patches also serve as main port of entry during typhoid fever, a disease caused Salmonella typhi in humans. The lpf operon encodes long polar fimbriae (LP fimbriae), which allow Salmonella typhimurium to adhere to murine Peyer's patches and are necessary for destruction of M cells. Fimbrial adhesins have very specific structural requirements for recognition of epithelial surface epitopes, thereby restricting bacterial binding to cell populations carrying the optimal receptor epitope. This is referred to as tropism and partly determines the niche a pathogen is able to occupy. The long term objective of this study is to understand the mechanisms which contribute to the tissue tropism of S. typhimurium for Peyer's patches. The study of binding properties of the adhesin encoded by the lpf operon and the identification of the cell type it binds in the epithelium of murine Peyer's patches are the main focus of this research. The aims of this research are: (I) To gain insight as to how LP fimbriae bind to murine Peyer's patches, the subunit of LP fimbriae mediating adhesion will be identified and its binding properties will be studied in vitro and in vivo. (II) To increase our understanding of how S. typhimurium adheres to the surface of Peyer's patches, the cell type to which LP fimbriae bind in the follicle associated epithelium will be identified. In particular, Dr. Baumler will investigate whether the lpf fimbrial operon of S. typhimurium mediates binding to M cells or a different target in Payer's patches. S. typhimurium is both an important human pathogen and the basis for live attenuated vaccine carrier strains. This study will provide knowledge about the tropism of S. typhimurium for gut associated lymphoid tissue, which is of value for both areas of research. The investigator's results will therefore facilitate both the design of improved attenuated vaccines and the development of new strategies to prevent disease caused by this pathogen. Understanding of the tissue tropism of S. typhimurium in the intestine will in addition provide fascinating new insights into how this and other enteroinvasive pathogens cause disease.